As serious as the earthquake- and tsunami-caused damage to the Fukushima Daichi nuclear power reactors is proving to be, the lessons learned can point the way to safer nuclear power in the future.

That is the opinion of Jor-Shan Choi, a world-recognized expert in nuclear safety. Recently returned to the Bay Area after three years teaching nuclear sociology at Tokyo University, Choi described the situation at Fukushima and offered his views on a path forward with regard to spent fuel at a recent seminar sponsored by the Global Security principal directorate.

Prior to his Tokyo University position, he worked at LLNL for nearly 20 years on projects in nuclear criticality safety, nuclear nonproliferation and the HEU downblending program, and alternative nuclear fuels. Choi also spent three years at the International Atomic Energy Agency (IAEA). Currently, he is affiliated with the Berkeley Nuclear Research Center at UC Berkeley.

When the double-blow disaster struck on March 11 -- a magnitude-9 earthquake followed by a 14-meter-high tsunami -- Choi was 500 kilometers south in Kyoto at a workshop that he had organized on international cooperation with regard to nuclear power plant safety, security and safeguards.

In providing a brief chronology of events at Fukushima Daichi's units 1 through 4, he observed that "the current situation is static but not stabilized." According to Choi, the nuclear reactors survived the earthquake and automatically shut down as they were supposed to do. But the tsunami ripped away the seawater pumps that cooled the plants' residual-heat-removal systems, leading to core overheating, partial fuel melting, hydrogen explosions and radioactive releases into the surrounding area.

"Heat buildup is the problem, and the cooling systems are absolutely critical," he observed. Boiling water reactors, like those at Fukushima Daichi, use controlled nuclear fission to generate heat that turns water to steam, which turns steam turbines to generate electricity. The steam then condenses back into water, which in turn helps cool the reactor core. Loss of cooling resulting from loss of electrical power and circulating pumps (as happened at Fukushima) is a death knell for a nuclear reactor.

The first explosion occurred at Unit 1 on March 12, one day after the earthquake and tsunami. Explosions occurred at Unit 3 two days later on the March 14 and at Units 2 and 4 on March 15. Choi explained that two types of explosions are possible --  a steam explosion or a hydrogen explosion. The latter is much more serious, as it indicates that the zircaloy cladding on the fuel rods has been breached (i.e., melted). The force of the explosions, particularly at Unit 3, and the subsequent detection of airborne radioactivity point to hydrogen explosions.

Unlike the reactors in Units 1, 2 and 3, which were operating when the disaster struck, Unit 4's reactor was shut down. However, the Unit 3 explosion was so severe that it also damaged Unit 4, resulting in the loss of cooling water from that unit's spent fuel pool. The source of the hydrogen for the Unit 4 explosion is not entirely clear; it could have resulted from overheated spent fuel rods in the emptied pool or, as is currently suspected, from Unit 3.

Faced now with the meltdown of three reactor cores, plant owner Tokyo Electric Power Co. (TEPCO) must devise some way to enclose the damaged cores. "The first priority is to build long-term cooling systems for Units 1, 2 and 3, and this will take six to nine months or more."

Although nuclear power accounts for nearly one-third of Japan's energy production, Choi noted that the Japanese public has a largely negative view of nuclear power. "Japan is the only country to have been attacked by nuclear weapons. They have a victim's mentality with regard to things nuclear."

In addition, Choi explained that prior to the situation at Fukushima Daichi, a number of accidents and incidents had tarnished nuclear power in the eyes of the Japanese public, including a sodium leak at the Monju breeder reactor in 1995, a fire and explosion at the Tokai reprocessing plant in 1997, a criticality accident also at Tokai in 1999 that caused several deaths, and scandals involving falsified mixed oxide fuel data in 2000 and boiling water reactor safety inspection reports in 2002.

Because of Fukushima, the future of nuclear power in Japan is uncertain. If the country backs away from nuclear power, Choi believes it will likely turn to Russia for energy imports. Given the long history of contentious relations between the two countries, "this would be a major geopolitical change."

Looking ahead, Choi stated "Fukushima is a critical event in that we have to learn from it. We have to use Fukushima as an opportunity to make changes for the future use of nuclear energy."

The major unresolved problem -- the elephant in the room, as it were -- is what to do with spent nuclear fuel. In the U.S. alone, 65,000 tons of spent fuel are in temporary storage in wet pools or dry casks.

"We need a cradle-to-grave plan for nuclear fuel," said Choi, "but we have no grave. Without a grave, nuclear power is constipated with used fuel and high-level waste."

He pointed out that mined repositories are very expensive, partly because they have to be very large to dissipate heat. "Yucca Mountain is as large as Singapore, and there's already more than enough U.S. nuclear waste to fill it completely."

Choi offered a new paradigm for spent fuel disposal. "Advanced partitioning and deep borehole disposition is a workable option," he asserted.

This approach hinges on the fact that the problematic components of spent fuel - those that are heat-producing or long-lived - are a small fraction of the total spent fuel, about half a percent by weight.

By separating the various spent fuel components, they can be disposed of in a manner that addresses their specific characteristics and hazards.

Uranium makes up 95.6 percent of spent fuel and can be recycled for use in reactors.

Stable short-lived isotopes make up 3 percent and can be disposed as low-level waste.

Plutonium and the other transuranics (1 percent) can be collected together with the heat-producing cesium and strontium isotopes (0.3 percent) for self-protection. At an appropriate time in the future, the transuranics can be separated out and recycled for use in reactors, and the cesium and strontium can be disposed of in deep boreholes.

Long-lived isotopes of iodine-129, technetium-99 and neptunium-237 (0.1 percent) can be separately encapsulated and disposed of deep boreholes.

By separating out the various components of spent fuel, the volume of waste that requires permanent disposal in deep boreholes is greatly reduced. "We'd be dealing with volumes measured in cubic meters, not repositories the size of Singapore," said Choi.

"This country's fixation on plutonium has dictated U.S. spent fuel storage policy for more than 30 years. It's true that there are proliferation concerns, but they can be managed."

He readily acknowledged that research is needed to study the advanced partitioning and deep borehole concept but insisted that the problem is workable.

"The country and the world need nuclear energy. Just as Fukushima needs an ultimate heat sink for cold shutdown and recovery, nuclear energy needs a grave to deal with its spent fuel and high-level waste."

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